In the field of microcontroller units (MCUs) employing clocked circuits/signals it is known that the synchronous logic circuits introduce limitations with respect to the voltage and temperature operating range dependent upon the clock frequency employed in the MCU. The term synchronous logic circuit generally encompasses any clocked logic circuit where logic signals are propagated through a circuit in response to a plurality of timing signals, such as trigger signals or a variety of clock signals.
In low voltage or high temperature states, during for example MCU initialisation or controlled power down of the MCU, the MCU needs to be maintained in a fully functional state. When clocked (synchronous) logic is used for such functional operations, a specific range of voltage and temperature is specified, with no performance guarantees provided outside of this range. Notably, the guaranteed performance associated with synchronous logic is limited to a narrow supply voltage range. There is therefore a need for the MCU to exhibit deterministic behaviour at a lower voltage than the point at which the MCU is fully operational.
However, it is known that operating conditions of voltage and temperature regularly exist that fall outside of this normal operating range.
Many MCU applications require compliance with stringent safety standards, such as EN60730,which demand deterministic behaviour in all conditions. There is therefore a need for the MCU to exhibit deterministic behaviour at a lower voltage than the point at which the MCU is fully operational. For example, MCUs need to support safety modes during start-up, power down and in response to unexpected external events.It is known that some techniques exist to minimise risks of incorrect MCU operation at low operating voltages, such as providing a watchdog function or provide low voltage interrupt (LVI) functions. These functions provide some protection, but are known to also suffer the same limitations that the MCU suffers from. For example, if the design of the MCU is based on clock signals, then single point failures are still possible and the operation of the MCU is more or less the same for the watchdog as it is for the rest of the MCU.
United States Patent U.S. Pat. No. 5,350,407 A describes a mechanism to asynchronously control singular events. For example, on Column 3 line 8-52, a use of external asynchronous circuits is used to control a behaviour of a second circuit. All of the circuits are applied at a high system-board level and constitute a very low level of asynchronous control. The decision making process is restricted to a singular analogue event with no ‘intelligent’ behaviour other that pre-defined and constructed. Furthermore, for example in Column 6 line 53 to column 7, line 22, a use of wakeup circuits is used to initiate operation of the Microcontroller. These circuits are again external to the microcontroller and behave in an ‘asynchronous’ manner. In addition, for example in Column 9, line 33-line 39, a discussion of a use of a low voltage detector to protect memory operation is provided. Further, for example in Column 10, line 59 to column 11, line 3, a use of a low voltage detector to protect memory and register operation is described. It also describes the interaction of the reset control function.
United States Patent U.S. Pat. No. 5,350,407 A also describes, for example in Column 14, line 22-line 39, a use of a low voltage detector to minimise power supply as the voltage level deteriorates. This helps set different levels of operation for the safe level of the RAM memories. Furthermore, for example in Column 17, line 33 to column 18, line 50, a discussion of a Power on reset operation, and how its behaviour is controlled by an asynchronous state machine, is described. Again the asynchronous logic is outside the microcontroller.
United States Patent Application Publication US 2003/110403 A1 describes a use of a power sharing circuit to match required power against specific load conditions. Intelligent power management exists in many systems today, where loads are monitored and then power scaled accordingly.
Thus, a need exists for an improved MCU and method of operation therefor.